Fast switched pulsed radio frequency amplifiers

ABSTRACT

A switching system is connected to the power amplifier of an RF system. The switching system can switch the DC supply voltage to the power amplifier while handling the high DC current and the nanosecond switching speed requirements that are mandatory for most RF systems. The embodiments can rapidly control DC voltages but not interfere with the optimized operation of the RF transistor. The embodiments provide a desired sharp turn-on leading edge for an RF pulse while eliminating the extremely long and undesirable ramp down that typically occurs beyond the desired RF pulse period.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefits of and priority, under 35U.S.C. § 119(e), to U.S. Non-Provisional application Ser. No.15/583,484, filed May 1, 2017, entitled “FAST SWITCHED PULSED RADIOFREQUENCY AMPLIFIERS,” which is incorporated herein by reference in itsentirety for all that it teaches and for all purposes, and to U.S.Provisional Application Ser. No. 62/329,559, filed Apr. 29, 2016,entitled “SWITCHING METHOD TO MITIGATE HEAT IN TRANSISTOR BASED PULSEDRF POWER AMPLIFIERS,” which is incorporated herein by reference in itsentirety for all that it teaches and for all purposes, and to U.S.Provisional Application Ser. No. 62/486,214, filed Apr. 17, 2017,entitled “SWITCHING METHOD TO MITIGATE HEAT IN TRANSISTOR BASED PULSEDRF POWER AMPLIFIERS,” which is incorporated herein by reference in itsentirety for all that it teaches and for all purposes.

FIELD

The present disclosure is generally directed to power amplifiers, inparticular, toward controlling power amplifiers in radio frequency (RF)systems.

BACKGROUND

RF systems, for example, Doppler Radar used for tracking weathersystems, include power amplifiers to drive the signal sent from theantennae. Doppler Radar and other similar RF systems may send a pulsedRF signal. To generate the pulsed RF signal, a pulsed RF power amplifiermust change power from a direct current (DC) power supply into thepulsed signal by changing the signal with RF transistors.

Amplification of low power signals is a cornerstone of many modern radiofrequency devices. Examples include pulsed telemetry, radar, electroniccountermeasures, and other applications including electronic warfare.Solid state power amplifiers used in RF applications can vary fromsingle transistor designs to multiple combined transistors to meetspecific power requirements of system designers.

Gallium Nitride devices are now the top choice for the power transistorsdue to their very high efficiency and long life. The typical structureof a transistor is a semi-conducting material located on substrate witha minimum, but not limited to, three connections to the electricalcircuit. Two architectures commonly used in RF transistors are bipolarjunction transistors (BJTs) and Field Effect Transistors or (FETs). Theconnections associated with BJTs are usually labeled as Emitter, Base,and Collector, while FETs label the circuit connections as Gate, Source,and Drain. Transistors used in amplifying circuits have outputs higherthan the respective inputs. In current RF transistor designs, typicallya negative voltage is applied to the Gate connection, the Source isgenerally connected to the ground or return, and the Drain is the highervoltage and higher current that powers the transistor.

Generally, the Drain side of the transistor is continuously powered,which creates heat, uses a large amount of power, and generates signalnoise in the signal. The Gate function, or switch side in an RF deviceacts to limit current to a prescribed value to protect the device fromself-destruction and additionally provides the low signal RF input. Inan RF FET, the Gate side of the transistor also serves as the RF inputwhile the drain is the output. Voltages applied to the Gate are referredto as a bias. The control voltages may be positive or negative withrespect to the Source or return.

Semiconductor device manufactures publish specifications regarding theproper bias for FETs. An example of this specification would be a commonRF FET having a Drain supply voltage of 50 volts DC and a Gate voltageof negative 2.7 volts that limits the current that is drawn on the Drainside of the transistor. A proper Gate voltage provides the bestefficiency and the longest life.

Semiconductor designs can be optimized for operation in certain areas ofthe radio frequency spectrum. This design optimization may be both acritical requirement and a detriment. In a typical high power microwaveamplifier, many stages of gain, or amplification, are required toproduce a meaningful outcome signal. The multi-gain stage designsintroduce significant noise into the system. During operation within acircuit, without any RF signal present, transistors create noise oroscillate within the desired band of operation and continue to drawoperating current from the DC power supply while no signal is presentfor amplification (known as the inter-pulse period). Amplifier designersnow rely on the integration of high power RF switches to address thisnoise.

These RF switches are very expensive and consume valuable space withinthe amplifier. In addition, the RF switches lack the power handlingrequired. The other major undesired result of using the RF switches isthe heat generated by the devices, which requires thermal managementsystems and techniques. A typical high-gain, high-power, solid-sateamplifier can use large high-surface area heatsinks with fans to movethe required volume of air needed to cool the RF switches. Some powersolid state amplifiers may require complex and problematic liquidcooling systems consisting of pumps, tubing, and radiators. Thesecooling systems are large, heavy, and potentially complex, withreliability and maintenance issues.

The basic transistor structure above has several issues. As mentionedabove, the Drain side of the transistor is powered continuously, whichis problematic. The presence of this continuous power results in highheat, high current consumption, and unwanted noise—all significant andunavoidable problems.

Using the pulsed radar amplifier as an example, an approach might be toturn the transistor completely off during the non-pulse period, orintra-pulse period. Since pulsed signals have a short duration, e.g., innanoseconds, the requirements of switching the transistor arechallenging. Previous approaches have been to switch the gate side ofthe transistor between the optimum value for best efficiency and a fullrail voltage to completely shut off the RF flow thru the transistor.Since the gate control voltages and current are much lower than thedrain side, attempts to enhance performance with this method wereunsuccessful. At the maximum gate bias the transistor continued tocreate noise. Switching the high voltage high current drain sideeffectively shuts down the transistor. A solution had to be realizedusing an ultra-fast DC switch that would perform at both the speed andhigh current required. Thus, there is still a need to create a switchingsolution for the above problems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an environment including one or more RF systems inaccordance with embodiments of the present disclosure;

FIG. 2 is a block diagram of an RF system in accordance with at leastsome embodiments of the present disclosure;

FIG. 3 is a block diagram of an RF system with a drain switching circuitin accordance with at least some embodiments of the present disclosure;

FIG. 4 is a circuit diagram of the RF power amplifier in accordance withembodiments of the present disclosure;

FIG. 5A is a first portion of a circuit diagram of the drain switchingcircuit connected to the RF power amplifier circuit in accordance withembodiments of the present disclosure;

FIG. 5B is a second portion of a circuit diagram of the drain switchingcircuit connected to the RF power amplifier circuit in accordance withembodiments of the present disclosure;

FIG. 5C is a third portion of a circuit diagram of the drain switchingcircuit connected to the RF power amplifier circuit in accordance withembodiments of the present disclosure;

FIG. 6 is a signal diagram showing the triggering on of the RF poweramplifier in accordance with embodiments of the present disclosure;

FIG. 7 is a signal diagram showing the triggering on and off of the RFpower amplifier in accordance with embodiments of the presentdisclosure;

FIG. 8 is a signal diagram showing the triggering on of the RF poweramplifier in accordance with embodiments of the present disclosure;

FIG. 9 is a signal diagram showing the triggering on of the RF poweramplifier in accordance with embodiments of the present disclosure;

FIG. 10 is a process diagram showing a method for switching on and off aRF power amplifier in accordance with embodiments of the presentdisclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a letter thatdistinguishes among the similar components. If only the first referencelabel is used in the specification, the description is applicable to anyone of the similar components having the same first reference labelirrespective of the second reference label.

DETAILED DESCRIPTION

The embodiments presented herein help resolve some or all three ofissues with the development of a very fast, high speed, high current DCswitching circuit that powers the drain supply circuit of a RF poweramplifier transistor. The embodiments described herein provide theadvantages of significantly reducing the size and weight of the powersystems needed to drive RF transmissions.

Generally, neither metal oxide semi-conductor field effect transistors(MOSFETs) or perhaps an isolated gate bipolar transistor (IGBTs) canremedy the above problems. Unfortunately, neither of the above devicedevices has the speed required to switch the DC drain current on and/oroff and are not in a usable form factor or package. Recent developmentsin Gallium Nitride technology provided in some of the latest RF GalliumNitride FETs (GaNFETs) have provided possibilities of solving some ofthe issues in RF systems, such as providing a novel, purpose builtswitch circuit to turn on and off the drain supply of the RF poweramplifier transistors. The high speed GaNFET switch very effectivelysolves the high thermal output, high current consumption, noise, and thesize and weight issues.

The novel and unobvious switching system described herein had to addressthe high DC current handling and the nanosecond switching speedrequirements that are mandatory for most RF systems. The embodimentsherein had to rapidly control DC voltages but not interfere with theoptimized operation of the RF transistor. It was discovered duringdevelopment of the GaNFET switch that, due to the capacitance of theGaNFET and the slow decay of energy after voltage had been switched off,undesirable characteristics of the pulsed signal were created. Theembodiments provided the desired sharp turn-on leading edge for thepulse while an extremely long undesirable ramp down occurred beyond thedesired RF pulse period.

Most FET's incorporated into switching power supplies, lamp dimmers,inverters, or motor speed controls can work well in applications withpoor trailing edge characteristics explained above, but do not meet therequirement of a typical RF circuit. To better shape the pulsed signal,a secondary GaNFET was added in a H Bridge circuit to discharge theremainder of the stored charge energy in the RF transistor after thedesired pulse period.

To be a viable solution as a fast DC switch specific for a RFapplication, the embodiments herein provide a fast ramp on and ramp offtimes, in the order of nanoseconds, without leading edge overshootringing that is typical in switching circuits. Timing of the GaNFETON/OFF is critical for both system performance and to preventself-destruction of the DC FET switch. The elimination of stored energyafter the desired RF pulse was a critical step in achieving a workingcircuit. In application, the remaining energy held within the RFtransistor had to be taken directly to ground to realize a useablefalling edge of the pulsed signal. Lab testing has shown that during theOFF cycle of the switched pulse as much as 2.5 amps was discharged over10 nanoseconds. The decoupling circuit was adjusted to provide both thebest pulse shape and long term survivability of the DC FET switch.

Multiple methods have also been developed to control the switchedamplifier, for example, a control circuit can use fixed value componentsof the GaNFET driver, an advanced control that may incorporate aprogrammable logic device (PLO), a micro controller, and/or a fieldprogrammable gate array (FPGA). When the control scheme is implemented,dynamic adjustment of the switching circuit is possible to compensatefor different responses from a multitude of available and future RFtransistors or advances made to the GaNFET switches themselves. Suchprogrammable control additionally adjusts for manufacturing variance.

To control the pulsed RF amplifier, a system trigger may be introducedeither internally or externally by, for example, the radar master clock,a signal processor, and/or a system trigger derived from detectedincoming RF pulses. The “detected pulse” approach constantly monitorsthe input RF signal and amplified RF signal output to automaticallytrigger the amplifier and GaNFET switch. A processor can monitor systemtiming, amplifier response, duty cycle limit protection, voltage alarms,and gain values to adjust for optimum performance of the RF system.

Integration of the amplifier into any system design is possible as thedesign is flexible. Operation of the switched amplifier can be used toswitch either a continuous wave (CW) RF input, or Gate a pulsed RF inputsignal. This feature can eliminate the requirement of any RF switchingahead of the amplifier if a pulsed output is desired and only a CWsource is available.

The size, weight, power consumption, and unwanted RF noise have been aserious limiting factor for current RF systems. Many of thecurrently-available pulsed amplifiers exhibit noise during the timebetween pulses (known as the Intra-pulse interval). The noise in currentsystems can have a significant impact when such amplifiers are a part ofsensitive system, such as a Doppler radar. Current radar system mustsample the system noise, then use the sampled value to establish a zerosignal over noise ratio. Depending on the amplitude of the introducednoise, a sensitive receiver in a current radar system may suffersignificant loss in low end sensitivity and loss of overall dynamicrange. The embodiments herein eliminate or substantially reduce thenoise introduced by the RF power amplification.

The embodiments herein can yield significant benefit in both thermalmanagement, reduction of phase noise in the RF output signal, andsignificant reduction of required operating current. Tests on at leastsome of the embodiments presented herein have also shown significantreductions in both generation of waste heat and requirement of largehigh current DC power supplies. The significance of these reductionsbecome apparent when a radar system onboard of any type of aircraft orUAV, or spacecraft is restricted by form factor (physical size andweight), available power budget of the vehicle, and coolingrequirements. Modern radar system design has been moving in thedirection of placing critical RF components on the antenna structure toeliminate traditional losses associated with long lengths oftransmission line, wave guide, or coax. Currently available high-poweredsolid-state transmitters were of an unusable size and weight toincorporate on an antenna or for anything other than ground basedsystems. can enable further advancement in future system architecturefor phased-array radars and other systems.

The embodiments herein can switch a solid-state power amplifier (SSPA)that may include at least one transistor having a gate, a source, and adrain. A DC supply may be selectively connected to the drain that usinga pair of GaNFET switches configured in a traditional H-Bridge circuitconfiguration. The GaNFET switches provide a very rapid “turn-on” of theRF transistor drain circuit, and/or a rapid quench, or dump to groundwhen the RF transistor drain circuit is “turned off.” The RF transistorand the associated RF to DC de-coupling circuits have characteristicsclosely resembling a capacitor. Requirements for radar pulses, forexample, require steep ramping of the turn on (the leading edge of thesignal), and the turn off (the trailing edge of the signal) of DCvoltages that supply the drain side of the RF transistor such that allstored energy is expended at the end of the desired pulse. The GaNFETswitches provide this rapid on and off of the DC voltage at the drain ofthe amplifier.

Other components of the RF amplifiers include a DC power supply thatprovides required voltages to the system components that can include avoltage regulator, an inverting supply used for transistor bias (gatevoltage), a transistor drain through the GaNFET switch (switched DC),control and monitoring circuitry including, for example, logic devices(PLD or FPGA) and/or possibly outside connections, Ethernet and/orserial control. Other components may include RF transmission linesbetween RF components, which can include Wave Guide, Coax, Micro-strip,and or Strip-line, an RF power divider network, an RF power combinernetwork and matching circuitry, an RF circulator and/or isolator,resistors, capacitors and inductors, and chokes required for systemcontrol and de-coupling of RF from DC, and/or a mechanical housing thatadditionally provides RF shielding to the outside environment. Examplecircuitry is provided hereinafter.

With the high-speed switched transistor drain circuitry, the embodimentsherein can eliminate waste heat, which has significant impact on thearchitecture of RF transmitter designs. For example, existing highpowered solid state amplifiers, with four phase combined channelsincorporating RF transistors, may each draw one amp of current with adrain supply voltage of 50 volts, or generate 50 watts of power. The sumof the heat across the four channels would be 200 watts of dissipatedwaste heat. Not exceeding the transistor's manufacture's guidelines(typically 25-degrees C.) for baseplate temperature is paramount toensure the long life of the device. Based on the temperature rise andvariances in ambient temperature, a very large surface area for thebaseplate is required, along with forced air or a liquid cooling means,to mitigate the generated heat in current RF designs.

The embodiment herein of the solid state high power amplifier (SSHPA)has unmatched efficiency based upon the ability to control the ON timeof the RF transistors through the use of a high-speed on/off switchingmechanism. The result of this high-speed switching significantly reducesenergy consumption, eliminates waste heat and its detrimentaldistortion, and significantly improves power efficiency in the pulsedamplifiers. The size of the DC power supply can be greatly reduced by afactor of four. These methodologies also solve the challenges of thermalmanagement. The minimal waste heat can eliminate the need for heatsinks. These design changes allow for a crucial and significantreduction in the overall weight and size of the amplifier allowing forintegration into systems with tight constraints such as airborne orspace-borne platforms.

Significantly, current solid state amplifiers cannot achieve the higherpower densities. Pulsed radar performance is dependent on fulfillment ofthe required gain and power output. An additional requirement is verylow phase noise to enable enhanced detection of targets with very lowamplitude signatures with Doppler velocity detection well under currentthresholds. The embodiments provided herein can achieve the higher powerdensities matching or exceeding traditional vacuum tube microwavedevices with these new methodologies.

Further, the switching methods herein greatly reduces the waste heatproduced by an RF transistor, which may then be dissipated into theamplifier structure rather than a heatsink. The target temperaturemanufacturers typically use is 25° C. base plate temp for optimal lifeand performance. The maximum life of a transistor is based onmaintaining and/or not exceeding this temperature. The embodimentsherein greatly improve the life expectancy of a transistor because thistemperature is not exceeded or approached.

Our switching method also can allow the system to turn off thetransistor at a predetermined the right time to reduce noise at thetrailing end of the pulse. This change in switching the transistor offre-defines the intra-pulse noise floor. The resultant noise reductionallows detectability and sensitivity measurements not capable withprevious designs. The deduction in noise greatly benefits end usersusing the radar for surveilling, searching, and characterizing weathersystems that need to lower the Doppler detectability threshold.

In some configurations, a programmable logic device (PLD) or FPGA cancontrol the GaNFET DC drain switching. When using a PLD or FPGA tocontrol the GaNFET DC switch, the FPGA's or PLD's internal logic andmonitoring of parameters, for example, temperature, voltage, current,input and output RF characteristics, can control the operation of theGaNFET DC switch. Control of the GaNFET switch through the PLD or FPGAallows for dynamic compensation of the amplifier performance over a widevariance of operating conditions. This flexibility also allows the useof a multitude of different RF transistors in the design of theamplifier based on the ability to program the PLD or FPGA with theoperating characteristics of the transistor.

The embodiments herein are not only an amplifier but a switch too. Thesedesigns compensate for poor legacy components that may be noisy, adjustsfor a wide variance of ambient conditions, is self-monitoring, and iseasy to integrate for the end-user. Importantly, the embodiments nowalso precisely monitor the duty-cycle of the transistor and can preventthe transistor from exceeding the maximum design rating.

An embodiment of an environment 100 for providing RF communications orsignals may be as shown in FIG. 1 . In the environment, an antenna 104,112 may provide or transmit an RF signal. The RF signal may be projectedtowards a recipient, for example, a spacecraft 108 or other antenna (notshown). In some examples, the antenna 112 may project an RF pulsedsignal towards a weather system or storm cloud 120 and receive signalsback to determine a Doppler shift in the reflected signal for weatheranalysis.

The environment 100 can include different types of RF signal includingpulsed RF signaling, which may be used in at least some of the followingdescription. The RF antennas 104, 112 may be powered by a power supply116 a, 116 b. The power supply 116 can provide the desired gain insignal strength to the antenna 104, 112. The gain may be generatedthrough a series of power amplifiers as explained hereinafter.

An example of an RF system 200 (which is provided for explanationpurposes and is not limiting to the RF systems that may employ the poweramplification circuitry described hereinafter) may be as shown in FIG. 2. The RF system 200, shown in the example in FIG. 2 , may be a simplediagram for a Doppler radar system. The RF system 200 can receive amaster system clock signal from a master reference clock 204. The clocksignal may be received from some source or generated by an oscillator orother component. For the present example, the master reference clock maybe a 10 MHz system clock. The 10 MHz signal may be provided to a localreference oscillator 208.

The local reference oscillator 208 provides for the reference signal tobe provided to the single-sideband (SSB) upconverter 212 and to thereceiver subsection 236 for processing of a received signal. Inelectronics, a local reference oscillator 208 provides the signal, “LoIn” 210, that is used with a mixer to change the frequency of a signal.The frequency conversion process, also called heterodyning, produces thesum and/or difference frequencies from the frequency of the localoscillator and frequency of the input signal. Processing a signal at afixed frequency gives a radio receiver/transmitter improved performance.In many receivers/transmitters, the function of the mixer is provided ina converter, for example, the SSB upconverter 212.

An intermediate frequency digital receiver (IFDR) 216 may provide theintermediate frequency 214 into the single-sideband upconverter 212. Anintermediate frequency (IF) is a frequency to which a carrier wave isshifted as an intermediate step in transmission or reception. The IF iscreated by mixing the carrier signal, provided as or with an outsidecontrol signal 218, with a local oscillator signal 210 in a processcalled heterodyning, resulting in a signal at the difference or beatfrequency. Intermediate frequencies are used in RFtransmitters/receivers, in which an outgoing/incoming signal is shiftedto an IF for amplification before final transmission/detection is done.

Here, the single-sideband converter 212 may mix the reference signal 214with the Lo In signal 210 and then upconvert the mixed IF signal. In RFcommunications, single-sideband modulation (SSB) mixes the Lo In signal210 having a specific frequency, the carrier wave, with the signal to bebroadcast, signal 214. The result is a set of frequencies with a strongpeak signal at the carrier frequency, and smaller signals from thecarrier frequency plus the maximum frequency of the signal, and thecarrier frequency minus the maximum frequency of the signal. That is,the resulting signal has a spectrum with twice the bandwidth of theoriginal input signal. The mixed-frequency signal may then be providedto the driver amplifier 224 of a transmitter subsection 220.

The driver amplifier 224 can be a driver for the power amplifier circuit228 and/or an initial amplifier for the mixed signal. Thus, the driveramplifier 224 can be an electrical circuit or other electronic componentused to control the power amplifier 228. For example, the driveramplifier 224 may be a specialized integrated circuit that controls thehigh-power switches in the switched-mode power converters of the poweramplifier 228. Further, the power amplifier 224 can ramp up theamplitude of the mixed signal before being further amplified by themulti-stage power amplifier 228 (final stage amplification).

The mixed signal may then be provided to the power amplifier 228, undercontrol of the driver amplifier 224. In many configurations, the poweramplifier 228 may be a multi-stage power amplifier, which can amplifythe signal up to a desired gain in two or more stages. In other words,the power amplifier 228 may comprise two or more amplifiers thatsuccessfully amplify the input signal up to a desired gain. Each poweramplifier 228 can be a RF power amplifier that converts a low-powerradio-frequency signal into a higher power signal. Typically, RF poweramplifiers drive the antenna 240. As explained previously, RF poweramplifiers are designed to meet requirements such as gain, power output,bandwidth, power efficiency, linearity (low signal compression at ratedoutput), input and output impedance matching, heat dissipation, etc. Anexample of a RF power amplifier circuit 228 may be as described inconjunction with FIG. 3 .

The amplified signal may then be sent to a power coupler 232. The powercoupler 232 can provide a power sample to the receiver section 236through a mixer. Further, the power coupler 232 can be used to tune theantenna 244. The amplified signal for transmission may then be sentthrough a circulator 240 to the antenna 244. Any received or reflectedsignal may be received through the antenna 244 and the circulator 240switch to provide the received signal to the receiver subsection 236.The receiver subsection 236 may then provide the received signal througha limiter, low-noise amplifier, image rejection mixer, etc. into theintermediate frequency digital receiver 216. The IFDR 216 may thenanalyze and/or send the signal to outside processing.

An embodiment of the RF transmitter subsection 220, connected to theswitching system 302 may be as shown in FIG. 3 . This combination of theRF circuitry 220 and switching circuitry 302, shown in the circuit 300,may provide the high-speed switching necessary as describedhereinbefore.

An embodiment of the switched RF circuitry 300 may be as shown in FIG. 3. First, the RF signal 304, which may be a pulsed or CW signal, canenter a preamplifier 308 to increase the gain of the signal 304. Apreamplifier 308 “pre-amp” is an electronic amplifier that converts aweak electrical signal into an output signal strong enough to benoise-tolerant and strong enough for further processing, e.g., forsending to a power amplifier and an antenna. Without the pre-amp 308,the final signal at the antenna 244 may be noisy or distorted afterpower amplification. A bandpass filter 312 can then condition the signalfrom the pre-amp 308 to eliminate any noise or harmonics already presentin the signal. The driver amplifier 224 and/or multi-stage amplifier 228then amplify the signal to reach a desired gain before transmitting thesignal through the antenna 244. An example of a stage of the amplifier228 may be as shown in FIG. 4 .

The switching circuitry 302 can switch the DC voltage provide to thepower amplifiers 224/228 used to increase the gain of the input signalbefore transmission through the antenna 244. A reference signal ortrigger source 316 can trigger the circuit 302. In some configurations,the trigger source 316 may be an external trigger from a systemprocessor. For example, upon determining that an RF communication besent, a system processor can send a transistor-transistor logic (TTL)signal to the dual Schmitt trigger buffer 320 to begin switching of theDC voltage to the power amplifiers 224/228. In other configurations, aRF envelope detector 348 can receive an input RF signal and identify aleading edge of the RF envelope. For example, the RF envelope detector348 can be RF detectors, part number LTC5583, manufactured by LinearTechnologies, Inc. of Milpitas, Calif. The RF envelope detector 348 cansend a signal to a controller 356, upon detection of the RF envelope, totrigger the switching circuit 302.

The controller 356 may be a programmable logic device (PLD), amicroprocessor, an application specific integrated circuit, a FPGA, etc.As a PLD, the controller 356 need not include an onboard memory toexecute a programming logic. As such, the PLD may have advantages in theembodiments herein for use in space or other hostile environments wherememory can be corrupted. Regardless, the controller 356 can control allor some of the components of the switching circuit 302.

The PLD 356 will be used to describe the controller 356, but thecontroller 356 is not so limited and may comprise other types ofprocessors or controllers as described above. The PLD 356 can forcetriggering of the switching circuit 302. For example, the PLD 356 canreceive a signal indicating the detection of the RF envelope from the RFenvelope detector 348. From this information, the PLD 356 may send asignal to an output buffer 344. The output buffer 344 can time triggerssent to the dual Schmitt trigger buffer 320. The output buffer 344,therefore, may be some type of cache, memory, or other circuit used totime and trigger the Schmitt trigger buffer 320.

The voltage regulator 352 may also input information to the PLD 356. Thevoltage regulator 352 may also provide a set voltage to be provided tocircuit components and/or the PLD 356, which then could be used fortriggering the output buffer 344. Further, there may be controlinformation provided to the PLD 356 from the voltage regulator 352regarding the performance of the switching circuit 302.

The dual Schmitt trigger 320 can receive signals in analog form andconvert those to digital form for provision to the IC gate(s) 324 a, 324b. An example of the dual Schmitt trigger buffer 320 and relatedcircuitry may be as described in conjunction with FIG. 5A. Generally, aSchmitt trigger 320 is a comparative circuit that has a positivefeedback loop. The Schmitt trigger 320 can convert an analog inputsignal to a digital output signal. Thus, the dual Schmitt trigger buffer320 can receive an analog trigger source signal 316, such as an RFsignal, and create a digital output based on that analog RF signal input316. The Schmitt trigger 320 may also have different levels for outputthat can be custom-provisioned to create a predetermined RF envelope fortriggering the switching of the DC voltage source 340 that is providedto the amplifiers 224, 228. Thus, the Schmitt trigger 320 can create anon state before the RF pulse signal needs to be sent and an off stateafter the RF pulse has been sent. As such, the envelope for providing DCvoltage to the radio frequency subsection 220 may be larger than theactual pulse signal, ensuring that the entire pulse is sent duringamplification, or may be custom designed based on the requirements forthe RF transmission. The dual Schmitt trigger 320 may provide thedigital output to one or more integrated circuit (IC) gates 324 a, 324b.

The IC gates 324 can be a “not AND” (NAND) circuit. A NAND gate 324 canimplement logic for NAND function. In other words, the NAND gate 324 isan inverted AND gate, where, if both signals are low, the NAND gate 324outputs a high signal and, if both gates are high, the NAND gate outputsa low signal. If the inputs are different, then the output is also highsignal. An example of the IC NAND gates 324, and the related circuitry,may be as described in conjunction with FIG. 5B. The NAND gates 324 canoutput signals to a high-side/low-side gate driver 328.

The high-side/low-side gate driver 328 can receive a signal(s) from theNAND gates 324 and amplify those inputs to drive the switches 332, 336,which are shown as GaNFETs. The high-side/low-side gate driver 328 cantrigger the “on state” GaNFET 332 and/or the “off state” GaNFET 336. Anexample of the high-side/low-side gate driver 328, and the associatedcircuitry, may be as shown and described in conjunction with FIG. 5B.

A voltage regulator 360 may provide DC voltage to the IC gates 324 andthe high-side/low-side gate driver 328. The voltage regulator 360provides a steady DC voltage at a predetermined level. For example, theDC voltage may be +12 to +15 volts DC. The voltage regulator 360 mayalso be in communication with the PLD 356 or voltage regulator 352.

The switching circuit 302 can include one or more switches 332, 336. Insome configurations, the switches 332, 336 may be transistors, forexample, field effect transistors (FETs). In further configurations, theswitches 332, 336 are Gallium Nitride FETs (GaNFETs). Regardless, theswitches 332, 336 must switch high-voltage, high-current loads, 40+voltsand one amp or more. These high voltages are required by the amplifiers224, 228 to increase the gain of the signal being sent to the antenna244. Further, the switches 332, 336 must be capable of handling todissipate high current while switching at high speeds and/or in shorttime periods, for example, in under 100 nanoseconds. Thus, the switches332, 336 must meet the above or similar parameters, which allows theswitches to be used to switch an RF power amplifier. An example of theswitches 332, 336 may be as shown and described in conjunction with FIG.5C.

Hereinafter, an example RF amplifier 224, 228, with an example switchingcircuit 302, is provided in FIGS. 4 through 5C. The example circuit inFIGS. 4 through 5C is designed for a pulsed Doppler radar operating at1-2 GHz and 1000 Watts, through the power amplifier stages 224, 228. Itshould be noted that the circuit 300 is not limited to the circuitconfigurations shown in FIGS. 4 through 5C but may be changed to meetmany different RF designs, requirements, configurations, etc. Thus, thecircuit configurations shown in FIGS. 4 through 5C may have specificcapacitance, resistance, and/or inductance values as shown in FIGS.4-5C. However, these values are based on a particular designspecification and may be changed as understood by skilled in the art.However, this circuit gives an example to those skilled in the art tobetter explain the switching circuit described herein.

An example embodiment of one possible power amplifier circuit that maybe in the multi-stage power amplification 228 or driver amplifier 224may be as shown in FIG. 4 . An input RF signal 420 may enter the circuit224/228, an isolator 408 may then isolate the power amplifier circuit224/228 from other circuitry connected before the isolator 408. Theisolator 408 may be, for example, a C2ZE2 circulator manufactured bySonoma Scientific Inc. of Minden, Nev. With the load resistor 410connected to the circulator 408, the circulator 408 becomes the isolator408.

The output from the isolator 408 enters an impedance matching network412, with a capacitor and resistor. The impedance matching network 412helps match the impedance of the input circuitry to the output impedanceof the RF circuit 224/228, and, as such, the values of the resistor andcapacitor are specific to the implementation of the RF amplifier 224/228and the RF system 200. The output of the matching network 412 enters aDC blocking capacitor 414 before entering the power amplifier 404.

The power amplifier 404 may be a FET, as shown in FIG. 4 . An example ofthe power FET 404 can be part CGHB 35-400F, which is an RF MOSFETmanufactured by Wolfspeed, the RF division of Cree, of Durham, N.C. Thedrain 406 of the FET 404 may be connected to a 50V DC source 428. The DCsource 428 may be provided by the switching circuit 302, which isdescribed in more detail in FIGS. 5A through 5C. Thus, the weak RFsignal 420 is sent through the FET 406 and is amplified with a gain of10 or more decibels. The output is then sent through another isolator416, which isolates the power amplifier 404 from downstream circuitry,before being output through output 424 to either another poweramplification stage, in a multi-stage amplifier 228, or to thecirculator 240 and on to the antenna 244. The inductors and capacitorscircuitry 432, from the 50V input source 428 to the drain of the FET404, can isolate the RF side, shown in FIG. 4 , from the DC side of thecircuit, provided by the switch 302 at connection 428.

An example of the switching circuit 302 may be as described inconjunction with the FIGS. 5A through 5C. Thus, each of the circuitsshown in FIGS. 5A through 5C are portions of the same circuit 302connected in succession as shown in FIG. 3 . The dual Schmitt triggerbuffer 320 may be as shown in FIG. 5A. A pin header 504 can be connectedto a trigger source (not shown) and receive a trigger signal. Thetrigger signal 316 can be sent from a system trigger or may be a signalsent from the RF envelope detector 348 or some other component. Thetrigger 316 can be a 5 v TTL signal, or some other type of signal. Thesignal 316 enters the Schmitt trigger 320, and is output as a 5 vdigital trigger signal outgoing to help trigger the switches 332, 336.Only one side of the dual Schmitt trigger buffer 320 may be used. Thus,the Schmitt trigger 508 may be the only side used in the part shown inFIG. 5A. An example of a Schmitt trigger 508 may be part number4748C2G17, which may be a dual non-inverting Schmitt trigger, providedor manufactured by Nexperia Incorporated of Nijmegen, Netherlands. Thedigital trigger signal output from the Schmitt trigger 508 may then besent on to the IC gates 324 a and 324 b, which are shown in FIG. 5B.

The IC gates 324 can be NAND gates, for example, part number NC7SCO8L6X,manufactured by Fairchild Semiconductor of Sunnyvale, Calif. The NANDgate 324 provides for the output, a gate driver signal, to thehigh-side/low-side gate driver 328 and ensures switching to the highsignal at the correct input. The gates 324 provide for a gate driversignal as described in conjunction with FIG. 3 and allow for the propersignaling of the gate driver 328.

The gate driver 328 is operable to drive the switches 332 and 336. Anexample of the gate driver 328 may be part number LM5113SD, which is ahalf-bridge gate driver for enhanced mode GaNFETs, manufactured by TexasInstruments of Dallas, Tex. The high output (Hi signal) of the gatedriver 328 may be provided through resistor network 512 to the on GaNFET332, which functions as the switch to provide the 50V DC power to thepower amplifier 404. The low output (Low signal) of the gate driver 328controls the off state GaNFET 336, which rapidly drives the voltage atthe drain 406 of the power amplifier MOSFET 404 to ground. Examples ofthe switches 332 and 336 may be as shown in FIG. 5C.

As shown in FIG. 5C, the switches 332 and 336 can be transistors, forexample, GaNFETs. The GaNFETs are exemplary switches, but provide thenecessary characteristics for high-speed switching at high current andvoltage for the power MOSFET 404. An example of the switches 332, 336may be part number EPC2031, which is an enhancement mode powertransistor, and is manufactured or provided by Efficient PowerConversion Corporation of El Segundo, Calif. The GaNFETs 332, 336 areconnected in a H-bridge configuration. In a H-bridge configuration, theGaNFETs 332, 336 can quickly switch the drain of the power MOSFET 404 to50 volts, and in the off state, quickly switch the voltage level todrive the drain voltage at the power MOSFET 404 to ground. The output ofthe H-bridge configuration may then be connected to the multi-stagephase combined final stage 228 or driver amplifier 224, as the 5 ov DCsource, as is shown in FIG. 5C and FIG. 4 . The other circuitry withinFIGS. 4-5C may be particular to the implementation of this circuit,which is for a pulsed Doppler radar. The circuit configuration may bechanged based on the particular requirements of some other systems andthus is not so limited to the circuitry, including the values, forresistors, capacitors, inductors, etc., presented in FIGS. 4 through 5C.

An embodiment of a signal generated by the circuitry, described inconjunction with FIGS. 2 through 5C, may be as shown in FIG. 6 . Thesignal diagram 600 includes a first portion of the RF signal 602, whichis near or substantially at ground. A leading edge 608 of a pulse in thesignal 602 may then be received, which is created by the switching ofthe on-state GaNFET 332 to provide 50V DC power to the MOSFET 404. Thepeak 612 of the signal 602 is then reached and the RF envelope isterminated. Thereinafter, the slow dissipation of the current may beshown by the curve 616 for the signal 602. As such, the pulse is not acomplete square wave, but has a trailing edge that is not succinct. Thesignal eventually returns substantially to ground, as shown in portion620. Thus, the signaling diagram of FIG. 6 shows the effects of notusing the off-state GaNFET 336 but does demonstrate the sharp and rapidincrease in gain from fast switching of the power from ground to 50Vwithout needing to maintain the drain voltage at or near 50V DC. Thetiming of the signal shown in FIG. 6 may be in milliseconds or less,which demonstrates the quick transition to the on state.

A representation of the drain voltage at the transistor 404 may be asshown in FIG. 7 . The signal 702, at the drain 406, may first beprovided near or substantially at ground, as shown in portion 704.However, as shown in FIG. 7 , there may be noise within the signal 702,but the noise level is de minimus and causes no issues for the detectionor transmission of the RF signal. Before beginning the RF envelope, asindicated by dashed line 708, the GaNFET 332 is switched on, providing aleading edge 716 of the DC voltage signal pulse 702, at the drain 406 ofMOSFET 404. This leading edge 716 rises to a peak voltage level 720before the beginning of the RF envelope, represented by line 708. The DCvoltage signal is provided until after the RF envelope ceases,represented by line 712. The trailing edge 724 of the signal 702,created by switching off the on state GaNFET 332 and turning on the offstate GaNFET 336, shows the quick dissipation of the current and voltageat the drain 406. The GaNFETs 332, 336 provide a a sharp trailing edge724, which brings the signal voltage DC substantially back to ground, asshown in portion 728 of signal 702. Thus, the power to the MOSFET 404 israpidly turned off, while quickly establishing and maintaining thevoltage level during RF envelope.

The resultant RF signal 802 produced by the MOSFET 404, controlled bythe switching of the DC voltage at the drain 406, may be as shown inFIG. 8 . Here, the initial portion 604 of the signal 602 is shown nearor substantially at ground, however, containing some negligible noise. Arapid transition to the on state is shown, with a leading edge 608 ofthe pulse occurring with nanoseconds. The peak gain 612 is realizedduring transmission of the signal 802 and maintained for a period oftime (e.g., 10 microseconds). The falling edge 804 is reached and thesignal rapidly drops near or substantially to ground in portion 620. Thefalling edge 804 of the signal 802 also occurs within nanoseconds. Thus,a near perfect square wave pulse is produced with nanosecond switchingbetween low and high states and between high and low states. Thiswaveform 802 ensures the benefits mentioned above with minimizing powerloss, minimizing heat generation, minimizing signal noise, etc.

An embodiment of a signal diagram 900 that shows the signal 904 forswitching on of the on state GaNFET 332 and the signal 908 for theswitching off of the off state GaNFET 336 is shown in FIG. 9 . As shown,the on state GaNFET 332 is triggered on at some time before the offstate GaNFET 336 is turned off, shown in section 912. This overlappingof signals ensures that the DC voltage will not be applied across one ofthe GaNFETs 332, 336 causing a short or failure and allows the GaNFET332, 336 to reach the desired operating characteristics at theappropriate time.

An embodiment of a method 1000 for switching the RF power amplificationstage 224, 228 may be as described in conjunction with FIG. 10 .Generally, the method 1000 begins with a start operation 1004 andterminates with an end operation 1036. While a general order for thesteps of the method 1000 are shown in FIG. 10 , the method 1000 caninclude more or fewer steps or arrange the order of the stepsdifferently than those shown in FIG. 10 . The method 1000 can, at leastpartially, be executed as a set of computer-executable instructions,executed by a device, e.g., a PLD, or by a computer system or otherprocessor, and encoded or stored on a computer readable medium. Further,the method 1000 can be executed by a gate(s) or other hardware device orcomponent in an Application Specific Integrated Circuit, a FieldProgrammable Gate Array, or other type of hardware device. Hereinafter,the method 1000 shall be explained with reference to the systems,components, circuits, signals, etc. described herein with reference toFIGS. 1-9 .

In step 1008, an input signal is received by the RF system 200. Thisinput signal can be a system trigger to create or amplify a RF pulse orCW signal. The input signal can be used as a trigger source provided byan RF envelope detector 348, or provided as a trigger source 316. Thetrigger source 316 may then be provided to the switching circuit 302, instep 1012, which causes the triggering of the GaNFETs 332, 336 toprovide the high-DC voltage to the drain 406 of the power MOSFET 404.

In step 1016, the input signal provided at input 420 may then beamplified by a gain voltage being applied at the power amplifier 404.The gain voltage may effect a gain of 10 decibels or more. The gainvoltage, applied to the drain 406, then amplifies the input signal 420,in step 1020. It is possible that the output of a power amplifier 404may be provided as an output 424 into another power amplifier 404. Themulti-stages of power amplification may be as described in conjunctionwith component 228, in FIG. 3 , which can progressively increase thepower or gain of the output signal. The output signal may then be sentthrough a circulator 240 to an antenna 244 to be transmitted.

At some time thereinafter, the signal is terminated. The termination ofthe signal causes the GaNFET 332 to turn off, in step 1024, and causesthe contemporaneous GaNFET 336 to turn on, in step 1028. The switchingof the GaNFETs 332, 336 ceases the provision of the 50V DC gain voltageto the drain 406 of the MOSFET 404, in step 1032. With the switch ofthese GaNFETs 332, 336 shown in FIG. 5C, the voltage applied to thedrain 406 is quickly driven to ground. These steps create the squarepulse signal described in conjunction with FIG. 8 .

Any of the steps, functions, and operations discussed herein can beperformed continuously and automatically.

The exemplary systems and methods of this disclosure have been describedin relation to radar systems. However, to avoid unnecessarily obscuringthe present disclosure, the preceding description omits several knownstructures and devices. This omission is not to be construed as alimitation of the scope of the claimed disclosure. Specific details areset forth to provide an understanding of the present disclosure. Itshould, however, be appreciated that the present disclosure may bepracticed in a variety of ways beyond the specific detail set forthherein.

Furthermore, while the exemplary embodiments illustrated herein show thevarious components of the system collocated, certain components of thesystem can be located remotely, at distant portions of a distributednetwork, such as a LAN and/or the Internet, or within a dedicatedsystem. Thus, it should be appreciated, that the components of thesystem can be combined into one or more devices, such as a server,communication device, or collocated on a particular node of adistributed network, such as an analog and/or digital telecommunicationsnetwork, a packet-switched network, or a circuit-switched network. Itwill be appreciated from the preceding description, and for reasons ofcomputational efficiency, that the components of the system can bearranged at any location within a distributed network of componentswithout affecting the operation of the system.

Furthermore, it should be appreciated that the various links connectingthe elements can be wired or wireless links, or any combination thereof,or any other known or later developed element(s) that is capable ofsupplying and/or communicating data or electricity to and from theconnected elements. Transmission media used as links, for example, canbe any suitable carrier for electrical signals, including coaxialcables, copper wire, fiber optics, etc.

While the flowcharts have been discussed and illustrated in relation toa particular sequence of events, it should be appreciated that changes,additions, and omissions to this sequence can occur without materiallyaffecting the operation of the disclosed embodiments, configuration, andaspects.

A number of variations and modifications of the disclosure can be used.It would be possible to provide for some features of the disclosurewithout providing others.

In yet another embodiment, the systems and methods of this disclosurecan be implemented in conjunction with a special purpose computer, aprogrammed microprocessor or microcontroller and peripheral integratedcircuit element(s), an ASIC or other integrated circuit, a digitalsignal processor, a hard-wired electronic or logic circuit such asdiscrete element circuit, a programmable logic device or gate array suchas PLD, PLA, FPGA, PAL, special purpose computer, any comparable means,or the like. In general, any device(s) or means capable of implementingthe methodology illustrated herein can be used to implement the variousaspects of this disclosure.

In yet another embodiment, the disclosed methods may be readilyimplemented in conjunction with software using object or object-orientedsoftware development environments that provide portable source code thatcan be used on a variety of computer or workstation platforms.Alternatively, the disclosed system may be implemented partially orfully in hardware using standard logic circuits or VLSI design. Whethersoftware or hardware is used to implement the systems in accordance withthis disclosure is dependent on the speed and/or efficiency requirementsof the system, the particular function, and the particular software orhardware systems or microprocessor or microcomputer systems beingutilized.

In yet another embodiment, the disclosed methods may be partiallyimplemented in software that can be stored on a storage medium, executedon programmed general-purpose computer with the cooperation of acontroller and memory, a special purpose computer, a microprocessor, orthe like. In these instances, the systems and methods of this disclosurecan be implemented as a program embedded on a personal computer such asan applet, JAVA® or CGI script, as a resource residing on a server orcomputer workstation, as a routine embedded in a dedicated measurementsystem, system component, or the like. The system can also beimplemented by physically incorporating the system and/or method into asoftware and/or hardware system.

Although the present disclosure describes components and functionsimplemented in the embodiments that may reference particular standardsand protocols, the disclosure is not limited to such standards andprotocols. Other similar standards and protocols not mentioned hereinare in existence and are considered to be included in the presentdisclosure. Moreover, the standards and protocols mentioned herein andother similar standards and protocols not mentioned herein areperiodically superseded by faster or more effective equivalents havingessentially the same functions. Such replacement standards and protocolshaving the same functions are considered equivalents included in thepresent disclosure.

The present disclosure, in various embodiments, configurations, andaspects, includes components, methods, processes, systems and/orapparatus substantially as depicted and described herein, includingvarious embodiments, subcombinations, and subsets thereof. Those ofskill in the art will understand how to make and use the systems andmethods disclosed herein after understanding the present disclosure. Thepresent disclosure, in various embodiments, configurations, and aspects,includes providing devices and processes in the absence of items notdepicted and/or described herein or in various embodiments,configurations, or aspects hereof, including in the absence of suchitems as may have been used in previous devices or processes, e.g., forimproving performance, achieving ease, and/or reducing cost ofimplementation.

The foregoing discussion of the disclosure has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the disclosure to the form or forms disclosed herein. In theforegoing Detailed Description for example, various features of thedisclosure are grouped together in one or more embodiments,configurations, or aspects for the purpose of streamlining thedisclosure. The features of the embodiments, configurations, or aspectsof the disclosure may be combined in alternate embodiments,configurations, or aspects other than those discussed above. This methodof disclosure is not to be interpreted as reflecting an intention thatthe claimed disclosure requires more features than are expressly recitedin each claim. Rather, as the following claims reflect, inventiveaspects lie in less than all features of a single foregoing disclosedembodiment, configuration, or aspect. Thus, the following claims arehereby incorporated into this Detailed Description, with each claimstanding on its own as a separate preferred embodiment of thedisclosure.

Moreover, though the description of the disclosure has includeddescription of one or more embodiments, configurations, or aspects andcertain variations and modifications, other variations, combinations,and modifications are within the scope of the disclosure, e.g., as maybe within the skill and knowledge of those in the art, afterunderstanding the present disclosure. It is intended to obtain rights,which include alternative embodiments, configurations, or aspects to theextent permitted, including alternate, interchangeable and/or equivalentstructures, functions, ranges, or steps to those claimed, whether suchalternate, interchangeable and/or equivalent structures, functions,ranges, or steps are disclosed herein, and without intending to publiclydedicate any patentable subject matter.

Embodiments include a radio frequency (RF) circuit, comprising: avoltage source that supplies gain voltage; a power amplifier; and aswitch electrically coupled to the voltage source, ground, and the poweramplifier, wherein the switch selectively applies the gain voltage tothe power amplifier and/or selectively applies ground to the poweramplifier.

Any of the one or more above aspects, wherein the power amplifier is aRF amplifier.

Any of the one or more above aspects, wherein the radio frequencyamplifier is a power RF metal oxide fiend effect transistor (MOSFET).

Any of the one or more above aspects, wherein the gain voltage isapplied to a drain of the power RF MOSFET.

Any of the one or more above aspects, wherein the voltage source is a DCvoltage source.

Any of the one or more above aspects, wherein the DC voltage sourceprovides the gain voltage over 40 volts.

Any of the one or more above aspects, wherein the switch comprises afirst on state switch and a second off state switch.

Any of the one or more above aspects, wherein the first on state switchis a Gallium Nitride field effect transistor (GaNFET) and the second offstate switch is also a GaNFET.

Any of the one or more above aspects, wherein the first on state GaNFETand second off state GaNFET are connected in a H-bridge configuration.

Any of the one or more above aspects, wherein the first on state GaNFETelectrically connects the power amplifier to the voltage source.

Any of the one or more above aspects, wherein the second off stateGaNFET electrically connects the power amplifier to ground.

Any of the one or more above aspects, wherein the first on state GaNFETswitches the gain voltage at the drain of the amplifier in less than 100nanoseconds.

Any of the one or more above aspects, wherein the second off stateGaNFET brings the drain to ground and dissipates a current at the drainin less than 100 nanoseconds.

Embodiments further include a method for controlling a radio frequency(RF) circuit, comprising: receiving a trigger signal; based on thetrigger signal, switching an on state GaNFET, electrically coupled to aRF power metal oxide fiend effect transistor (MOSFET) amplifier, toconnect a drain of the RF power MOSFET power amplifier to a DC voltagesource; amplifying an RF signal with the RF power MOSFET amplifier whilethe on state GaNFET 15 switched; ending an RF envelope; based on endingthe RF envelop: switching again the on state GaNFET; switching an offstate GaNFET, also electrically coupled to the RF power MOSFETamplifier, to drive the drain of the RF power MOSFET amplifiersubstantially to ground; and discontinuing amplification of the RFsignal with the RF power MOSFET amplifier.

Any of the one or more above aspects, wherein the power amplifier is aradio frequency (RF) amplifier.

Any of the one or more above aspects, wherein the DC voltage sourceprovides the gain voltage for the RF power MOSFET amplifier.

Any of the one or more above aspects, wherein the on state GaNFET andthe off state GaNFET are connected in a H-bridge configuration.

Any of the one or more above aspects, wherein the on state GaNFETswitches the gain voltage at the drain of the amplifier in less than 100nanoseconds.

Any of the one or more above aspects, wherein the off state GaNFETbrings the drain to ground and dissipates a current at the drain in lessthan 100 nanoseconds.

Embodiments further include a RF circuit, comprising: a poweramplification circuit comprising an RF power metal oxide fiend effecttransistor (MOSFET) comprising at least a gate, a source, and a drain,wherein the power amplification circuit amplifies a received RF signal;a DC voltage source providing a gain voltage; a ground; a switchingcircuit electrically coupled to the drain of the RF power MOSFET, theswitching circuit comprising: a Schmitt trigger to receive a triggersource and to convert the trigger source into a digital trigger signal;an IC gate electrically coupled to the Schmitt trigger to receive thedigital trigger signal and supply a gate trigger signal; a gate driverelectrically coupled to the IC gate to receive the gate trigger signaland to send a gate signal to a Hi gate signal and/or a Low gate signal;a first GaNFET electrically coupled to the gate driver, wherein, basedon receiving the Hi gate signal, electrically coupling the DC voltagesource to the drain of the RF power MOSFET to amplify the received RFsignal, wherein the first GaNFET switches the drain to the gain voltagein less than 100 nanoseconds; and a second GaNFET electrically coupledto the gate driver and electrically coupled to the first GaNFET in anH-bridge configuration, wherein, based on receiving the Low gate signal,electrically coupling the ground to the drain of the RF power MOSFET toceasing the amplification of the received RF signal, wherein the secondGaNFET drive the drain to the ground in less than 10 nanoseconds.

Any one or more of the aspects/embodiments as substantially disclosedherein.

Any one or more of the aspects/embodiments as substantially disclosedherein optionally in combination with any one or more otheraspects/embodiments as substantially disclosed herein.

One or means adapted to perform any one or more of the aboveaspects/embodiments as substantially disclosed herein.

The phrases “at least one,” “one or more,” “or,” and “and/or” areopen-ended expressions that are both conjunctive and disjunctive inoperation. For example, each of the expressions “at least one of A, Band C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “oneor more of A, B, or C,” “A, B, and/or C,” and “A, B, or C” means Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, or A, B and C together.

The term “a” or “an” entity refers to one or more of that entity. Assuch, the terms “a” (or “an”), “one or more,” and “at least one” can beused interchangeably herein. It is also to be noted that the terms“comprising,” “including,” and “having” can be used interchangeably.

The term “automatic” and variations thereof, as used herein, refers toany process or operation, which is typically continuous orsemi-continuous, done without material human input when the process oroperation is performed. However, a process or operation can beautomatic, even though performance of the process or operation usesmaterial or immaterial human input, if the input is received beforeperformance of the process or operation. Human input is deemed to bematerial if such input influences how the process or operation will beperformed. Human input that consents to the performance of the processor operation is not deemed to be “material.”

Aspects of the present disclosure may take the form of an embodimentthat is entirely hardware, an embodiment that is entirely software(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module,” or “system.”Any combination of one or more computer-readable medium(s) may beutilized. The computer-readable medium may be a computer-readable signalmedium or a computer-readable storage medium.

The terms “determine,” “calculate,” “compute,” and variations thereof,as used herein, are used interchangeably and include any type ofmethodology, process, mathematical operation or technique.

The term “radio frequency (RF)”, as referred to herein, may refer to anyof the electromagnetic wave frequencies that lie in the range extendingfrom around 3 kHz to 300 GHz, which include those frequencies used forcommunications or radar signals. RF usually refers to electrical ratherthan mechanical oscillations.

The term “H Bridge”, be an electronic switching circuit that enablesvoltages to be applied across a load in either direction.

The term “field effect transistor” (FET), as referred to herein, may bea transistor that uses an electric field to control the electricalbehavior of the device. FETs are also known as unipolar transistorssince FETs involve single-carrier-type operation. Many differentimplementations of FETs exist. FETs generally display very high inputimpedance at low frequencies. The conductivity between the drain andsource terminals is controlled by an electric field in the device, whichis generated by the voltage difference between the body and the gate ofthe device.

The term “metal oxide semiconductor field effect transistor” (MOSFET),as referred to herein, may be a type of FET. A MOSFET has an insulatedgate, whose voltage determines the conductivity of the device. Theability to change conductivity with the amount of applied voltage can beused for amplifying or switching electronic signals. Although FETs aresometimes used when referring to MOSFET devices, other types offield-effect transistors also exist. Although the MOSFET is afour-terminal device with source (S), gate (G), drain (D), and body (B)terminals, the body (or substrate) of the MOSFET is often connected tothe source terminal, making it a three-terminal device, like otherfield-effect transistors. Because these two terminals are normallyconnected to each other (short-circuited) internally, only threeterminals appear in electrical diagrams.

The term “Gallium Nitride field effect transistor” (GaNFET), as referredto herein, may be a FET manufactured using gallium nitride (GaN).

The term “power amplifier”, as referred to herein, may be an electronicdevice that can increase the power of a signal (a time-varying voltageor current). An amplifier functions by using electric power from a powersupply to increase the amplitude of the voltage or current signal. Anamplifier is effectively the opposite of an attenuator: while anamplifier provides gain, an attenuator provides loss.

The term “amplifier”, as referred to herein, may be either a separatepiece of equipment or an electrical circuit contained within anotherdevice. Amplification is fundamental to modern electronics, andamplifiers are widely used in almost all electronic equipment.Amplifiers can be categorized in different ways. One is by the frequencyof the electronic signal being amplified; RF amplifiers amplifyfrequencies in the radio frequency range between 20 kHz and 300 GHz.Another classification is by quantity of voltage or current beingamplified; amplifiers can be divided into voltage amplifiers, currentamplifiers, transconductance amplifiers, and transresistance amplifiers.A further distinction is whether the output is a linear or nonlinearrepresentation of the input. Amplifiers can also be categorized by theirphysical placement in the signal chain. Today most amplifiers usetransistors, but vacuum tubes continue to be used in some applications.

The term “multistage power amplifier”, as referred to herein, may be apower amplifier that amplifies in two or more stages. A single-stageamplifier is often insufficient for many applications; hence severalstages may be combined forming a multistage amplifier. These stages areconnected in cascade, i.e., output of the first stage is connected toform input of second stage, whose output becomes input of third stage,and so on.

The term “Schmitt trigger”, as referred to herein, may be a comparatorcircuit with hysteresis implemented by applying positive feedback to thenoninverting input of a comparator or differential amplifier. It is anactive circuit which converts an analog input signal to a digital outputsignal. The circuit is named a “trigger” because the output retains itsvalue until the input changes sufficiently to trigger a change. In thenon-inverting configuration, when the input is higher than a chosenthreshold, the output is high. When the input is below a different(lower) chosen threshold, the output is low, and when the input isbetween the two levels the output retains its value. This dual thresholdaction is called hysteresis and implies that the Schmitt triggerpossesses memory and can act as a bistable multivibrator (latch orflip-flop).

The term “decibel (dB)”, as referred to herein, may be a logarithmicunit used to express the ratio of two values of a physical quantity. Oneof these values is often a standard reference value (e.g., a voltage),in which case the decibel is used to express the level of the othervalue relative to this reference. When used in this way, the decibelsymbol is often qualified with a suffix that indicates the referencequantity that has been used or some other property of the quantity beingmeasured. For example, dBm indicates a reference power of one milliwatt,while dBV is referenced to 1 volt RMS.

The term “bias”, as referred to herein, may be a steady (DC) current orvoltage that some electronic devices require to operate correctly. An ACsignal applied to the devices can be superposed on this DC bias currentor voltage.

The term “R-C coupling”, as referred to herein, may be is the mostwidely used method of coupling in multistage amplifiers. In this case,the Resistance R is the resistor connected at the collector terminal andthe capacitor C is connected in between the amplifiers. It is alsocalled a blocking capacitor, since it will block DC voltage. The maindisadvantage of this coupling method is that it causes some loss for thelow frequency signals. However, for amplifying signals of frequenciesgreater than 10 Hz, this coupling is the best and least expensivemethod. It is usually applied in small signal amplifiers, such as inrecord players, tape recorders, radio receivers, etc.

In electronics, the term “gain”, as referred to herein, may be a measureof the ability of a two-port circuit (often an amplifier) to increasethe power or amplitude of a signal from the input to the output port byadding energy converted from some power supply to the signal. It isoften expressed using the logarithmic decibel (dB) units (“dB gain”).

In communications and electronic engineering, the term “intermediatefrequency” (IF), as referred to herein, may be a frequency to which acarrier wave is shifted as an intermediate step in transmission orreception. The intermediate frequency is created by mixing the carriersignal with a local oscillator signal in a process called heterodyning,resulting in a signal at the difference or beat frequency. Intermediatefrequencies are used in superheterodyne radio receivers, in which anincoming signal is shifted to an IF for amplification before finaldetection is done.

Conversion to an intermediate frequency is useful for several reasons.When several stages of filters are used, the filters can all be set to afixed frequency, which makes them easier to build and to tune. Lowerfrequency transistors generally have higher gains so fewer stages arerequired. It is easier to make sharply selective filters at lower fixedfrequencies. There may be several such stages of intermediate frequencyin a superheterodyne receiver; two or three stages are called double(alternatively, dual) or triple conversion, respectively.

The term “continuous wave” or “continuous waveform” (CW), as referred toherein, may be an electromagnetic wave of constant amplitude andfrequency; a sine wave.

What is claimed is:
 1. A radio frequency (RF) circuit, comprising: avoltage source that supplies gain voltage; a power amplifier; and aswitch electrically coupled to the voltage source, ground, and the poweramplifier, wherein the switch selectively applies the gain voltage tothe power amplifier and/or selectively applies ground to the poweramplifier, wherein the switch brings the power amplifier to ground anddissipates a current at the power amplifier in less than 100nanoseconds.
 2. The RF circuit of claim 1, wherein the power amplifieris a RF amplifier.
 3. The RF circuit of claim 2, wherein the radiofrequency amplifier is a power RF metal oxide field effect transistor(MOSFET).
 4. The RF circuit of claim 3, wherein the gain voltage isapplied to a drain of the power RF MOSFET.
 5. The RF circuit of claim 4,wherein the voltage source is a DC voltage source.
 6. The RF circuit ofclaim 5, wherein the DC voltage source provides the gain voltage over 40volts.
 7. The RF circuit of claim 6, wherein the switch comprises afirst on state switch and a second off state switch.
 8. The RF circuitof claim 7, wherein the first on state switch is a Gallium Nitride fieldeffect transistor (GaNFET) and the second off state switch is also aGaNFET.
 9. The RF circuit of claim 8, wherein the first on state GaNFETand second off state GaNFET are connected in a H-bridge configuration.10. The RF circuit of claim 9, wherein the first on state GaNFETelectrically connects the power amplifier to the voltage source.
 11. TheRF circuit of claim 10, wherein the second off state GaNFET electricallyconnects the power amplifier to ground.
 12. The RF circuit of claim 11,wherein the first on state GaNFET switches the gain voltage at the drainof the amplifier in less than 100 nanoseconds.
 13. The RF circuit ofclaim 12, wherein the second off state GaNFET brings the drain to groundand dissipates a current at the drain in less than 100 nanoseconds. 14.A method for controlling a radio frequency (RF) circuit, comprising:receiving a trigger signal; based on the trigger signal, switching an onstate GaNFET, electrically coupled to a RF power metal oxide fieldeffect transistor (MOSFET) amplifier, to connect a drain of the RF powerMOSFET power amplifier to a DC voltage source; amplifying an RF signalwith the RF power MOSFET amplifier while the on state GaNFET isswitched; ending an RF envelope; based on ending the RF envelop:switching again the on state GaNFET; switching an off state GaNFET, alsoelectrically coupled to the RF power MOSFET amplifier, to drive thedrain of the RF power MOSFET amplifier substantially to ground, whereinswitching the off state GaNFET brings the RF power MOSFET poweramplifier to ground and dissipates a current at the RF power MOSFETpower amplifier in less than 100 nanoseconds; and discontinuingamplification of the RF signal with the RF power MOSFET amplifier. 15.The method of claim 14, wherein the power amplifier is a radio frequency(RF) amplifier.
 16. The method of claim 15, wherein the DC voltagesource provides the gain voltage for the RF power MOSFET amplifier. 17.The method of claim 16, wherein the on state GaNFET and the off stateGaNFET are connected in a H-bridge configuration.
 18. The method ofclaim 17, wherein the on state GaNFET switches the gain voltage at thedrain of the amplifier in less than 100 nanoseconds.